1. Field of Invention
This invention relates to the decoding of a received logic signal to determine the correct logic state of individual signal bits, and more particularly to the determination of the mean voltage value of the operating logic voltage levels of the digital signal for use in decoding of the individual signal bits.
2. Description of the Prior Art
In digital systems wherein digital data is transmitted between distinctly separate units, it is sometimes impossible to ensure the maintenance of desired operating logic voltage levels due to operating conditions, such as severe environmental changes, power supply fluctuations or system inaccuracies. In addition, the transmission of digital data between units separated at great distances from each other, such as a sensing unit transmitting data to a remote processor where the data transmission is performed over a single line (as opposed to a two line differential transmission mode), requires that consideration be given to the effects of data distortion. Such distortion may be in the form of: induced noise causing variations in the operating logic voltage levels resulting in the inability to detect logic state transitions; attenuation of the logic voltage levels due to extensive line losses causing loss of granularity and inability to detect the attenuated logic states; or the effects of common mode voltage differences between the grounds of the two systems which causes the received data to become biased at voltage levels different from the transmitted operating logic voltage levels, creating similar difficulty in detecting the true logic states.
The decoding of digital data is of critical importance in digital systems in which the transmitted data pulse train includes timing synchronization pulses at amplitudes different from that of the data itself, to provide time synchronization between the units. Such a use of modified amplitude synchronization pulses within the data pulse train, provides a less complex method of time synchronization than those employing binary codes.
In all such instances, accurate reproduction of the data requires knowledge of the mean logic voltage level to ensure accurate decoding of the true logic state of the individual signal bits.